1. Field of the Invention
This invention relates generally to dispensing apparatus for a fluid under pressure, and more specifically, this invention relates to dispensing apparatus for a liquid under pressure that utilizes a piston to dispense a predetermined quantity of the liquid.
2. Description of the Prior Art
As pointed out in applicant's earlier U.S. Pat. No. 4,892,232, there are disadvantages to prior art finger operated pumps for dispensing a small amount of liquid from a container. In particular, one cannot count upon obtaining the same amount of liquid each time because the speed and the extent of stroke of the actuator affect the quantity of liquid dispensed.
In U.S. Pat. No. 4,892,232, an arrangement is provided for achieving the dispensing of a predetermined quantity of liquid with each actuation of the dispensing apparatus. In that device, a resilient and collapsible metering reservoir is positioned in the liquid under pressure. With that structure, it is possible to obtain dispensing of a substantially constant amount of the liquid upon each actuation of the dispensing apparatus. While this device is quite successful in dispensing the desired amount of liquid, there are instances in which it is preferable to achieve dispensing of a predetermined quantity of liquid using only mechanical elements rather than the elastomeric metering reservoir.